1. Field of the Invention
The present invention relates generally to a semiconductor package mounting technique and, more specifically, to high density vertical surface mount packages. More particularly still, the present invention relates to vertical surface mount devices having retention apparatus or devices for holding the package to a surface mount location.
2. State of the Art
Integrated circuit semiconductor devices are fabricated on wafers of silicon to generate semiconductor devices or chips. Each of these chips forms an integrated circuit semiconductor device that must be packaged in order to be utilized within a computer system. One type of package is to encapsulate the semiconductor device in a plastic package, in some instances, with the semiconductor device being bonded to a die paddle of a leadframe. The individual leads of the leadframe are then connected to bond pads on the active surface of the semiconductor device using wires with the units being encapsulated in a suitable plastic or similar material. This plastic encapsulated semiconductor device then undergoes a trim and form operation that separates the interconnected packages on leadframe strips into individual entities and then bends the exposed leads of the remaining leadframe extending from the package. This is the traditional and most recognized form of semiconductor device package and utilizes a highly automated manufacturing technology.
Several types of semiconductor device packages that have found favor include a package having dual in-line metal lead packages or DIP, which typically were through hole soldered onto a printed circuit board, and a pin grid array (PGA) package that includes a plurality of under-leads that are usually either through hole soldered to a substrate or inserted in a receiving unit. Additional types of semiconductor device packages include the ball grid array, which is soldered onto the surface of the printed circuit board. Additionally, a new type of dual in-line lead design has been provided and is known as the small outline J-Lead package (or “SOJ” package). The SOJ package has advantages over the standard DIP design for the following reasons. First, the leads of a SOJ package are soldered to only one side of the circuit board, thus leaving the other side of the board free for the mounting of additional SOJ packages. Second, the leads are much less vulnerable to damage prior to board assembly; hence, there are fewer rejections. The SOJ package has extended to include a zig-zag in-line package or ZIP and provides advantages of allowing the package to be mounted vertically. Vertical packages have a narrower horizontal cross section than the horizontally attached DIP or SOJ or PGA packages. Vertical packages allow the distance between other vertical packages to be quite minimal to the horizontal packages.
In ZIP packages or in vertical packages, all leads exit through the lower edge of the package. Since the vertical packages with a single edge being attached to the printed circuit board must be held in place before a solder reflow operation is performed, they have a limited appeal because of the difficulty in maintaining the vertical packages in such vertical position.
Solutions have been provided to allow for the positioning of ZIP vertical packaging without the need for additional package support structures until the final attachment of the package to the circuit board during a solder reflow operation.
One such example is described in U.S. Pat. No. Reissue 34,794 (“the '794 reissue patent”), reissued Nov. 22, 1994. The '794 reissue patent describes a semiconductor package having a gull-wing zig-zag, in-line lead configuration and package anchoring devices. The anchoring devices allow the semiconductor package to be rigidly fixed to a circuit board such that each lead resiliently contacts its associated mounting pad on the board. The particular anchoring device includes anchoring pins having fish-hook type bars that lock against the other side of the board when the pegs are inserted through the holes. Further, the anchoring pins can be adhesively bonded in recesses as provided in a circuit board. This type of arrangement has several disadvantages. The first disadvantage is that the printed circuit board or circuit board must include holes for receiving the anchoring devices. These holes may crack and cause the circuit board to split along such a fracture, thus ruining the board. Additionally, since the anchoring devices are inflexible, they too may fracture and break and thus release the semiconductor package that is in a bias tension against the circuit board because of the anchoring devices. Furthermore, the anchoring devices must extend out from either side of the semiconductor devices, which anchoring devices may require additional spacing, thus limiting the number of packages that can be vertically mounted on the circuit board.
Accordingly, an improved type of vertical package of the ZIP where the anchoring apparatus overcomes the problems inherent in the prior solution of the anchoring devices inserted into the circuit board is needed.